Method of purging fuel-supply system



Jan. 29, 1963 J. 5. IRWIN- El'AL METHOD OF PURGING FUEL-SUPPLY SYSTEM Filed July 27, 1960 /wv/v JAMES s. IRWIN and TORS v LAMBERT J. K/LBOY, Jr.

A Horny United States Patent 3,875,833 METHOD 0F PURGHNG FUEL-SUPPLY SYSTEM James S. Irwin, Rich Township, Cool; County, and Lamhart Ii. Kilboy, in, Worth Township, Cook County, 111., assignors to United States Steel Corporation, a corporation of New Hersey Filed Italy 27, 1969, Set. N 45,630 4 (Ilaims. (Cl. 48-190) This invention relates to a method of purging and returning combustion gas to a conduit system and more particularly to such a system utilizing blast furnace gas. In case of a plant shut down it is necessary to purge the blast furnace gas from the mains because air infiltration may cause an explosion and gas leaking from the mains may cause asphyxiation. The mains extend throughout the plant and during the purging process the transporting of hot ingots and the necessity of having workmen in the area increase the safety hazard. When production is resumed the blast furnace gas must be readmitted to the mains so as to service the various consuming units which use the gas for fuel such as steam boilers, gas engines and reheating furnaces. The prior method of purging consisted of opening the vent valves at the ends of the mains and introducing steam at one or more points into the main. Booster fans induced air into the mains and forced the steam and gas to the atmosphere through the vents. When operations were resumed steam was again introduced into the mains, after which blast furnace gas was introduced to displace the steam and air in the mains. This later was vented to atmosphere until all of the air was displaced by blast furnace gas. The vent valves were then closed and the mains were ready for operation. This method was relatively expensive and time consuming, especially when starting up, and left much to be desired from the standpoint of safety.

it is therefore an object of our invention to provide a method of purging and returning combustible gas to a conduit system without danger of explosion.

Another object is to provide such a method wherein starting up operations can be accomplished without the necessity of repurging the mains.

These and other objects will be more apparent after referring to the following specification and attached drawings, in which:

The single FIGURE is a schematic view of a conduit system wherein our method may be applied.

Referring more particularly to the drawings reference numeral 2. indicates a conduit system having branches 4-, 6, 8 and it Blast furnace gas or other combustible is introduced into the conduit system 2 from a supply main 12 through a valve 14. Vents i6, 18, 2t and 22 are provided at the end of each branch 4, 6, 8 and 14), respectively. If the combustible is blast furnace gas, coke oven gas, or any other gas that is lighter than the purging gas, the vents will be at the top of the branch conduits. Along each branch conduit is provided a load which uses the gas. For example, furnaces 24-, 26 and 28 may be arranged adjacent branches 4, 6 and 8 and a boiler or power station 3%) may be positioned adjacent branch 10. A purging gas conduit 32 is connected to the system through a valve 34 adjacent the point of connection of branch conduits 4, 6, 8 and ill.

In carrying out our invention the valve 14 is closed and the vents 16, 18, 2t and 22 open. Valve 34 is opened and carbon dioxide is introduced into the system through conduit 32. it is preferred that the CO be introduced at a point where the resistance to flow of CO will be equal in all directions. in some instances this may require the introduction of CO at more than one point. The venting is continued until a C0 concentration of at least 50% is 3575333 Patented Jan. 2%, 1963 ice obtained at the vents. For increased safety it is preferred that the CO concentration be at least 70% at the vents. The vents are then closed so the introduction of CO is continued until a positive pressure is obtained in the conduit system. For example, the pressure may be 10 inch water gauge. The flow of 00 is then shut off by closing valve 34 except when the shut down is to be for a short period of time and/or unless the system is an unusually tight one. From a practical standpoint it is rare that the system will be sufficiently tight to prevent leakage of pressurized gas from the conduit or leakage of air into the conduit when not under pressure. Shortly before the system is to be reactivated, the 00 content of the gases in the system is determined adjacent the vents and the pressure of the gases determined. If the CO content is at least 50% and there is a positive pressure the valve 14 is opened and the combustible gas is fed into the system. With the particular loads shown the vents need not be opened at this time since the gas in the system can be introduced into the burners and exhausted without danger. When a combustible mixture is obtained it will start to burn. When the tests indicate a C0 content of less than 50% adjacent the vents, the vent valves are opened and carbon dioxide again admitted until the CO content is above 50%. The vents are then closed, the CO shut off and blast furnace gas admitted to the system as set forth above. If the CO content is below 50% it is probable that the gases in the main have leaked from the system until the system is at atmospheric pressure and some air may have leaked into the system. It will be understood that other gases which are non-combustible and non-toxic and which remain in gaseous condition at atmospheric temperatures may be used in place of C0 The term non-combustible gas is meant to exclude those gases which support combustion.

While one embodiment of our invention has been shown and described, it will be apparent that other adaptations and modifications may be made without departing from the scope of the following claims.

We claim:

1. The method of purging and returning combustible gas to a conduit system comprising opening vents at selected points in the system to permit escape of combustible gas therethrough, introducing non-combustible gas which remains gaseous at atmospheric pressure into the system with the vents remaining open until the concentration of the non-combustible gas is at least 50% at the vents, then closing the vents and continuing introduction of the non-combustible gas until a positive pressure is obtained in the conduit system, testing the gases in the system for non-combustible gas content before reactivating the system, then introducing sufiicient non-combustible gas into the system to obtain a concentration of at least 50% non-combustible gas, and then introducing combustible gas to the system.

2. The method of purging and returning combustible gas to a conduit system comprising opening vents at selected points in the system to permit escape of combustible gas therethrough, introducing non-combustible gas which remains gaseous at atmospheric pressure into the system with the vents remaining open until the concentration of the non-combustible gas is at least 70% at the vents, then closing the vents and continuing introduction of the non-combustible gas until a positive pressure is obtained adjacent the vents, then shutting of the non-combustible gas, testing the gases in the system for non-combustible gas content and pressure before reactivating the system, then introducing non-combustible gas into the system until the concentration of the non-combustible gas is at least 70% and the gases are at a positive pressure in the conduit system, and then introducing combustible gas to the system.

3. The method of purging and returning combustible gas to a conduit system comprising opening vents at selected points in'the system to permit escape of combustible gas therethrough, introducing CO into the system with the vents remaining open until a C0 concentration of at least 50% is obtained at the vents, then closing the vents and continuing introduction of CO until a positive pressure is obtained in the conduit system, test- 10 ing the gases in the system for CO content and pressure before reactivating the system, then introducing CO into the system to obtain a positive pressure and a C0 concentration of at least 50% adjacent the vents, and then introducing combustible gas to the system.

4. The method of purging and returning combustible gas to a conduit system comprising opening'vents at selected points in the system to permit escape of combustible gas therethrough, introducing CO into the system with the vents remaining open until a C0 concentration of at least 50% is present at the vents, then closing the vents and continuing introduction of CO until a positive pressure is obtained adjacent the vents, then shutting off the CO testing the gases in the system for CO content and pressure before reactivating the system, then introducing CO into the system with the vents closed until a CO; concentration of at least 50% and a positive pressure is obtained in the conduit system, and then introducingcombustible gas to the system.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Trinks, Industrial Furnaces, vol. II, third edition,

20 1955, John 'Wiley a Sons, Inc., New York, page 350. 

1. THE METHOD OF PURGING AND RETURING COMBUSTIBLE GAS TO A CONDUIT SYSTEM COMPRISING OPENING VENTS AT SELECTED POINTS IN THE SYSTEM TO PERMIT ESCAPE OF COMBUSTIBLE GAS THERETHROUGH, INTRODUCING NON-COMBUSTIBLE GAS WHICH REMAINS GASEOUS AT ATMOSPHERIC PRESSURE INTO THE SYSTEM WITH THE VENTS REMAINING OPEN UNTIL THE CONCENTRATION OF THE NON-COMBUSTIBLE GAS IS AT LEAST 50% AT THE VENTS, THEN CLOSING THE VENTS AND CONTINUING INTRODUCTION OF THE NON-COMBUSTIBLE GAS UNTIL A POSITIVE PRESSURE IS OBTAINED IN THE CONDUIT SYSTEM, TESTING THE GASES IN THE SYSTEM FOR NON-COMBUSTIBLE GAS CONTENT BEFORE REACTIVATING THE SYSTEM, THEN INTRODUCING SUFFICIENT NON-COMBUSTIBLE GAS INTO THE SYSTEM TO OBTAIN A CONCENTRATION OF AT LEAST 50% NON-COMBUSTIBLE GAS, AND THEN INTRODUCING COMBUSTIBLE GAS TO THE SYSTEM. 